The present invention relates to an anti-friction bearing with a speed measuring device which employs an external high frequency wave transmitter and a receiver or other circuit which receives the signal from the transmitter. Means between the transmitter and the receiver and at the movable bearing ring alternately permit the waves to reach the receiver or block waves and the pulses are measured.
There is a need to provide many anti-friction bearings with means for detecting their speed of rotation. It is known to equip motor vehicle wheel bearings with speed detection, for instance, to derive the speed from signals obtained and to use it to control an anti-lock system. As it is desired to detect even low speeds of rotation, the sensor must be positioned at a very small distance from the pulse generator wheel or from a coding disk.
An anti-friction bearing having a pulse generating disk integrated in the seal of the bearing between the rings of the bearing is disclosed in DE 37 35 070 A1. However, the sensor must be spaced with a small air gap from the sealing disk, since the strength of the signal decreases as the square of the distance away.
U.S. Pat. No. 4,688,951 discloses an anti-friction bearing in which the electric signals are to be transmitted without contact. In this case, a sensor is arranged on the rotating bearing ring and transmits the electric signals to a receiver by capacitive or inductive changes in field or in the form of radio waves. The transmitter must be supplied with energy from a battery or a mini-generator. However, this is cumbersome, susceptible to faults and expensive.